The present invention relates to methods for making packaging bags, and more particularly to methods for making a flexible packaging bag for use with differently designed bagging machines,
Bags used in automated filling processes have been known for many years. Traditionally, these bags are produced from continuous sheets or rolls of bag material, typically organic or other plastic material. In many manufacturing processes, a sheet of bag material is folded and sealed to form a continuous flat bag tube having an upper and lower layer. This tube may be further folded or pinched to form multiple layers in, for example, side gusseted bags. The tube may then be again sealed, cut, stamped, separated, and stacked on storage wickets for subsequent use in the automated bag filling operation. Storage wickets onto which the newly formed bags are stacked are typically U-shaped pieces of thin rigid material, which fit through aligned wicket openings formed in the bags on the stack.
During bag filling, stacks of bags are transferred from the wickets onto mandrels which make up part of a bag filling mechanism. After the wicket is removed, the bags remain aligned and stacked on the mandrels. Typically, caps are then positioned over the exposed end of each filling mandrel thereby holding the stacked bags in formation so that they may be used in the filling operation.
During the bag loading process, suction cups or other grabbing means separate the upper layer of the bag from the lower layer, thereby initiating the opening of the bag. A jet or puff of air delivered through needle and check valve arrangements further opens the bag while the lower layer of the bag remains securely positioned on the filling mandrels. As the bag opens, loader arms unfold within the filling edge of the bag which open the bag completely, while a filling arm pushes items into the bag and ultimately pushes the filled bag off of the mandrel.
While wicketed bags represent a popular choice among manufactures in automated filling operations, such bags share a number of problems which have not been satisfactorily addressed at this time. One such problem stems from the difficulties associated with different types of bag opening and filling mechanisms. These bag opening and filling mechanisms can have various designs that can include differently shaped or designed parts or devices that handle the bags in a different manner. Thus, a bag that is designed and manufactured for one particular machine cannot be used on a differently designed machine that has parts or devices that prevent proper handling of the bag, such as, by way of example only, properly loading a wicket of bags on the machine, properly opening the bag, maintaining the bag in place during the filling process, pushing the bag out of the machine after it has been filled, or the like.
Due to the existence of differently designed bag filling mechanisms, an accompanying problem is the necessity of having to maintain dual, or more, inventories of items for differently designed mechanisms. This is costly because of having to purchase different bag designs and increased storage requirements.
In addition, known bags used in automated filling operations are problematic because of the substantial and non-uniform forces required to push the filled bag off the mandrel after loading. These forces, typically generated by the filling arm, involve breaking through a portion of the bag material between the wicket opening and the edge of the bag. Depending on the particular bag material being used, the force necessary to start the break, i.e., the initiation force, will vary substantially as the thickness and width of the material to be torn varies. In addition, the distance between the wicket opening and the filling edge of the bag, i.e., the width of the material to be torn, may vary in production bags, due in part to registration or positioning problems which may occur when the wicket opening and other cuts are made. As a result, the forces required to fill the bag, initiate the break and to continue the break, i.e., the propagation force, may vary not only from bag to bag, but within a given bag. These variations require different forces to be applied for different periods of time in order to fill the bag and ultimately push it off the mandrel at the appropriate time, which is after the bag is filled. The variations in forces can be extremely significant for certain types of bag materials such as, by way of example, low density polyethylene which has a propagation force curve which increases with the stretching of the material until a tear threshold is reached which occurs as the bag is pushed off the mandrel.
Yet another problem associated with wicketed bags of known construction is that the forces require to tear them from the filling mandrel often cause unwanted shards or fragments of bag material to tear and separate from the bag. These fragments are problematic in at least two ways. Loose fragments of material in a filled package are aesthetically unacceptable, and may be a safety hazard. Furthermore, these fragments of torn material often get caught and jam the bag filling mechanism causing significant downtime and increased cost of manufacturer.